Dating of buried wood logs and fragments for high resolution reconstruction of landslide histories: Case studies in the Japanese Alps region in the historical times
Ryuji YAMADA, Takashi KIMURA, Yoshihiko KARIYA, Masaki SANO, Akane TSUSHIMA, Zhen LI, Takeshi NAKATSUKA, Yoko SAITO-KOKUBU, Kimio INOUE
Establishing chronologies for large‐scale landslides is crucial to understand the cause of the mass movements and to take measures against potential hazards in future. We discuss the applicability of dating methods for determining landslide chronologies in relation to the type of samples and the stratigraphic setting of sampling location. Case studies are carried out with fossil wood samples buried in the deposits of large‐scale landslides in two areas of the Japanese Alps region in historic times; Dondokosawa rock avalanche (DRA) and Ohtsukigawa debris avalanche (ODA). Ages are determined by accelerator mass spectrometry radiocarbon dating and dendrochronological analysis using the oxygen isotope composition of tree ring cellulose. We report seven radiocarbon ages and five dendrochronology data for the wood samples taken from outcrops and excavated trenches in the lacustrine sediments of dammed lakes formed by DRA, and two radiocarbon ages and two dendrochronology data for wood samples of ODA. Two sets of data for DRA are crosschecked independently to ensure the accuracy of results. Most of ages in the DRA area are concordant with the period of AD887 Ninna (Goki‐Shichido) mega‐earthquake as proposed in previous studies. In the ODA area, ages are not concentrated in a specific period. When the preservation condition of buried wood trunks is good enough to date the exact or approximate tree‐death years dendrochronologically, it is possible to estimate landslide occurrence periods in further detail by comparing the landslide chronology with historical records of heavy rainfall and large earthquakes.
radiocarbon dating, dendrochronology, landslide history, Japanese Alps, oxygen isotope tree‐ring chronology, historical documents